The present invention relates to the sterilization of medical waste or more particularly to the sterilization of medical waste by use of a microwave autoclave wherein the waste material is subsequently readied for incineration or landfilling.
Medical waste is infectious refuse that can transmit disease. Medical waste generators include hospitals, doctors' offices, clinics, dental offices, laboratories, nursing homes, and funeral parlors. In addition, as medical costs rise, more long term illnesses are being treated at home and medical waste is thereby being mixed with ordinary household trash. In recent years the amount of medical waste has dramatically increased with the expanded use of disposable rather than reusable products. In addition, in many jurisdictions, the definition of medical waste has been broadened to include an ever widening variety of materials. The Center for Disease Control has issued recommended procedures whereby any material that comes into contact with any patient's body fluids be treated as if it were infectious. Examples of waste materials include bandages, gloves, tubing, syringes, laboratory cultures, and pathological wastes, among others. This waste is isolated in special sealed containers until they can be treated. Except for chemical treatment, all infectious bacteria, viruses and organisms are normally destroyed by some form of heat. The most widely used forms of treatment are autoclaving, or sterilization with steam, and burning at specially equipped incineration sites since most hospital incinerators do not meet pollution control and other regulatory standards. Retrofitting existing hospital incinerators or building new environmentally acceptable incinerators are extremely costly alternatives. On-site, low cost treatment of medical waste is very desirable.
The generally acknowledged most reliable method of sterilization is autoclaving, which entails the heating of items to at least about 212.degree. F. in a steam saturated atmosphere for periods of time ranging from about ten minutes to one day or more. Pressurized steam sterilization of instruments by autoclaving has been done by hospitals and medical offices for many years. However, the microwave autoclave sterilization of disposable medical waste has not been known heretofore. It is clear that large scale sterilization of medical waste is only possible if steam is able to penetrate bagged waste for a sufficient time at a sufficient pressure and temperature to effect essentially complete sterilization. In this regard a pressure vessel is required in order to achieve sterilization process as opposed to a vessel which is open to normal atmospheric conditions. After autoclaving or incineration, residues can be deposited in landfills. Another method of sterilization commonly used is dry heat, however, dry heat sterilization in ovens requires lengthy periods of heating. Other sterilization methods successfully used in limited situations include chemical vapor sterilization, bacteriocidal chemical treatment, and liquid disinfectant usage.
In response to an increase in illegal medical waste disposal, most States have issued statutes and regulations on the handling of medical waste both from large and small scale generators. In addition, the federal Medical Waste Tracking Act created a lifetime tracking system for infectious waste and before sterilized waste can be disposed of as non-infectious waste it must be rendered non-recognizable compared to its original form. The present invention provides a process for sterilizing infectious waste materials by subjecting them to a microwave autoclaving sterilization technique with subsequent granulation. The sterilization renders the waste non-infectious and the grinding yields a product which is non-recognizable as compared to its original form.
Sterilization by use of microwaves is per se known in the art for other applications. It is known that bacteria can be killed using microwaves, and that the effective mechanism by which this is accomplished is not entirely heat dependent. The microwave field effect itself is a contributing mechanism by which sterilization is accomplished. Thus, heating and drying by microwaves provides an advantage that ordinary heating and drying techniques cannot accomplish. In this regard, U.S. Pat. Nos. 3,880,586 and 3,885,915 each show an apparatus for sterilizing sealed, medicinal liquid filled ampules with microwave radiation. U.S. Pat. No. 3,955,286 similarly sterilizes ampules, except microwave irradiation is done in a hermetically sealed pressure vessel. U.S. Pat. No. 3,885,915 shows a method for the destruction of microorganisms in materials such as blood plasma and milk by a combination of ultraviolet and microwave radiation where the temperature is maintained below 100.degree. C. U.S Pat. No. 4,839,142 shows microwave pasteurization of biological fluids where the fluids are subsequently recovered. U.S. Pat. No. 3,955,286 shows sterilizing unfilled ampules using microwave radiation in a sealed vessel with repetitive pressure changes. U.S. Pat. Nos. 4,223,512; 4,250,139; 4,393,088; 4,400,401; 4,406,860; 4,406,861; 4,839,485 and 4,999,471 show microwave sterilization and heating of food and protein material. U.S. Pat. Nos. 4,614,514; 4,599,216; 4,671,935; 4,956,155; 4,971,773 and 5,019,344 show devices for microwave sterilizing items such as dialysis couplings, dentures, dental handpieces and contact lenses. U.S. Pat. No. 4,994,237 shows the microwave preservation of biological tissues such that tissue pliability and the qualities of natural, unpreserved tissue are maintained.
U.S. Pat. No. 4,896,010 shows a method of microwave drying and sanitizing fabrics. In this disclosure, a microwave field effect in combination with confined heated water below the boiling point sanitizes moist, bacteria laden fabrics. U.S. Pat. No. 4,935,114 shows a process for disposing toxic waste including chlorinated hydrocarbons by subjecting them to microwave radiation under conditions sufficient to break the hydrocarbon-chlorine bonds. U.S. Pat. No. 4,980,039 shows the degradation of halogenated hydrocarbon wastes by wet ashing with a reagent of 1:1 nitric acid and sulfuric acid and microwaving. None of these relate to medical waste treatment. U.S. Pat. No. 4,670,227 relates to steam sterilization of medical waste, however, such does not involve microwave irradiation to internally penetrate the waste as described below.
An important feature of any autoclave sterilization process is to provide verification that the waste has been retained at the requisite time and temperature to assure essentially complete sterilization. When using microwave techniques, heat is generated by penetrating and causing a vibration of the internal molecules of the waste. This shortens the time required to reach the temperature needed for sterilization. When non-homogeneous materials are microwave heated in the presence of water vapor, the high frequency provides moisture vaporization and a vapor transport dynamic unique to any other heat source including the simple introduction of steam. In the case of the usual autoclave, steam is introduced but is denied penetration due to mass permeability. As steam contacts the outer layer of the material, it condenses, transferring its thermal energy to the material being heated. It will continue this method of heating material sections from the outside in, as new external steam is applied and as the material permits. In order to revaporize the condensate in-situ, to promote continued internal migration, a method of internal heat dynamic is necessary. Artificial means of forcing steam into the core improve results, but are of limited ability to provide fast, even heat. Properly applied microwave heating provides this unique dynamic for the sterilization of medical waste. Electric field access to internal moisture instantly re-vaporizes condensate, thereby creating a continuous wave of internal steam. It is also known in the art to attempt to sterilize medical waste using microwave energy. In particular German patent application P3924744.9-41 shows a process for sterilizing medical waste where the waste is disposed in a hermetically sealed container, saturated with moisture via injection needles and microwaved in a tunnel. The container is then discharged from the tunnel. In this disclosure, sterilization occurs inside sealed plastic containers and not in a pressurized microwave chamber. This system is disadvantageous since the plastic container can degrade, melt or break and release the internal pressure and contaminate the inside of the chamber where the container is placed. In addition, if the pressure in the plastic container releases, sterilization conditions can no longer be insured. German patent 3833281 C1 shows a hermetically sealable waste container useful in the aforesaid process. Such a system is commercially available as Serifant 90 from Nordpunkt AG. This system does not provide means for granulating the medical waste and the container so that it is rendered unrecognizable and suitable for disposal as non-infectious material.
In a sterilization system commercially available from ABB Flaekt Sanitec GmbH, medical waste is first shredded, steam is introduced to supply moisture to the dry waste and then the waste proceeds along a screw where microwave energy is applied supposedly to complete sterilization. However, this method is disadvantageous because medical waste that is shredded before treatment can release airborne infectious organisms. Also, infected waste contaminates the shredders, augers and other internal parts of the machinery thereby preventing safe equipment maintenance. In addition, this open system does not contain steam in a pressure vessel so that a temperature sufficient for sterilization cannot be reached or maintained. This method is actually a system for disinfection, which is an incomplete sterilization. In addition, disinfection verification can only be done by sampling the material. A test vial of spores is introduced which can indicate whether the process was effective, but only after a twenty-four hour waiting period. This delay is impractical and does not allow the treated waste to be immediately taken away for incineration or landfilling.
This invention provides improved method for sterilizing medical waste by converting it into non-infectious material which is non-recognizable from its original form. This treated waste can then be disposed of much less expensively as ordinary trash such as by landfilling or burning in normal incinerators. The invention provides a process wherein medical waste is disposed in individual degradable containers, preferably composed of cardboard. The waste filled containers are positioned in a pressure vessel into which steam is injected. The vessel is then subjected to microwave radiation for a sufficient time and at a sufficient temperature and pressure to effect essentially complete sterilization of the waste and the container. In a subsequent step, both the waste and the container are shredded and/or granulated so as to render the product and container unrecognizable compared to the original items. Indicia are provided whereby sterilization is verified for each bag or individual container and a manifest is printed out to provide assurance that the required conditions were met to effect sterilization. The vessels are modular and can be ganged together to provide the desired throughput volume.